Harry Truman, having served as a judge, expressed an interest in running for the U.S. House of Representatives in 1934, but political bossTom Pendergast had already selected another candidate for that race. After four other potential candidates had declined to run, Pendergast ultimately approached Truman to discuss a possible run for the United States Senate, to Truman's surprise. Truman, with backing from Pendergast, entered the Senate race. Truman said he would not, if elected, dictate to anyone, to the dismay of anti-Pendergast U.S. Senator Bennett Champ Clark.
Truman waged a statewide campaign and eventually won the largely three-way Democratic primary on August 7, 1934, by a significant margin, defeating U.S. Representatives John Cochran and Jacob Milligan. After winning the Democratic nomination, Truman defeated Republican opponent and incumbent U.S. Senator Roscoe Patterson by a landslide margin of about 20% of the vote.